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How a Landfill Works Presented By: American Environmental Landfill, Inc

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How a Landfill Works Presented By: American Environmental Landfill, Inc How a Landfill Works Presented by: American Environmental Landfill, Inc. 1420 W. 35th Street, Suite B Tulsa, OK 74107 Phone: 918-245-7786 Fax: 918-245-7774 How a Landfill Works So you have just finished your meal at a fast food restaurant and you throw your uneaten food, food wrappers, drink cup, utensils and napkins into the trash can. Odds are you don’t think about that waste again. On trash pickup day in your neighborhood, you push your can out to the curb, and workers dump the contents into a big truck and haul it away. You don’t have to think about that waste again, either. But maybe you have wondered, as you watch the trash truck pull away, just where that garbage ends up. Americans generate trash at an astonishing rate of four to seven pounds per day per person, which translates to at least 600,000 tons per day or at least 210 million tons per year! This is almost twice as much trash per person as most other major countries. What happens to this trash? Some gets recycled or recovered and some is burned, but the majority is buried in landfills. In this overview of how a landfill works, we will examine how a landfill is made, what happens to the trash in landfills, what risks are associated with a landfill and how these risks are solved. How is Trash Disposed of? The trash production in the United States has almost tripled since 1960 (Figure 2). This trash is handled in various ways. About 27 % of the trash is recycled or composted, 16% is burned and 57% is buried in landfills. The amount of trash buried in landfills has doubled since 1960. The United States ranks about in the middle of the major countries (United Kingdom, Canada, Germany, France and Japan) in landfill disposal. The United Kingdom ranks highest, burying about 90 percent of its solid waste in landfills. 2 What is a Landfill? There are two ways to bury trash: • Dump - an open hole in the ground where trash is buried, often full of various pests and animals including rats, mice and birds. (This is most people’s idea of a landfill!) • Landfill - carefully designed structure built into or on top of the ground in which trash is isolated from the surrounding environment (groundwater, air, rain). This isolation is accomplished with a bottom liner and daily covering of soil. • Sanitary landfill - landfill that uses a clay liner to isolate the trash from the environment. • Municipal solid waste (MSW) landfill - uses a synthetic (plastic) liner to isolate the trash from the environment. The purpose of a landfill is to bury he trash in such a way that it will be isolated from groundwater, will be kept dry and will not be in contact with air. Unlike a compost pile, a landfill is designed to keep the trash away from people, but does not allow it to decompose quickly. Proposing the Landfill For a landfill to be built, the operators have to make sure that they follow certain steps. In most parts of the world, there are regulations that govern where a landfill can be placed and how it can operate. The whole process begins with someone proposing the landfill. In the United States, taking care of trash and building landfills are local government responsibilities. Before a city or other authority can build a landfill, an environmental impact study must be done on the proposed site to determine: • The area of land necessary for the landfill • The composition of the underlying soil and bedrock • The flow of surface water over the site • The impact of the proposed landfill on the local environment and wildlife • The historical or archaeological value of the proposed site Once the environmental impact study has been completed, permits must be obtained from the local, state and federal governments. In addition, money will have to be raised from taxes or municipal bonds to build and operate the landfill if it is owned by the government. In that case, funding will come from some public source; therefore public approval must be obtained through local governments or a referendum. Otherwise, landfills have to be constructed and managed by free enterprise and small business owners. 3 Building the Landfill Once the environmental impact study is complete, the permits are granted and the money has been raised (be it public or private funds), construction begins. First, access roads to the landfill site must be built if they do not already exist. These roads will be used by construction equipment, sanitation services and the general public. After roads have been built, then the landfill can be excavated. Parts of a Landfill This cross-section drawing shows the structure of a municipal solid waste landfill. The arrows indicate the flow of leachate, which is contaminated substances. The basic parts of a landfill, as shown in Figure 1, are: • Bottom liner system - separates trash and subsequent leachate from groundwater • Cells (old and new) - where the trash is stored within the landfill • Storm water drainage system - collects rain water that falls on the landfill • Leachate collection system - collects water that has percolated through the landfill itself and contains contaminating substances (leachate) • Methane collection system - collects methane gas that is formed during the breakdown of trash • Covering or cap - seals off the top of the landfill Figure 1 Structure of a Municipal Solid Waste Landfill; the arrows indicate the flow of leachate Each of these parts is designed to address specific risks that are encountered in a landfill. So, as we discuss each part of the landfill, we’ll explain what risk is solved. A Ground Water B Compacted Clay C Plastic Liner D Leachate Collection Pipe E Geotextile Mat F Gravel G Drainage Layer H Soil Layer I Old Cells J New Cells K Leachate Pond Figure 1 Structure of a Municipal Solid Waste Landfill; the arrows indicate the flow of leachate 4 Bottom Liner System A landfill’s major purpose and one of its biggest challenges is to contain the trash so that the trash doesn’t cause problems in the environment. The bottom liner prevents the trash from coming in contact with the outside soil, particularly the groundwater. In MSW landfills, the liner is usually some type of durable, puncture-resistant synthetic plastic (polyethylene, high-density polyethylene, polyvinylchloride). It is usually 30-100 mils thick. The plastic liner may be also be combined with compacted clay soils as an additional liner and surrounded on either side by a fabric mat (geotextile mat) that will help to keep the plastic liner from tearing or puncturing from the nearby rock and gravel layers. Cells (Old and New) Perhaps, the most precious commodity and overriding risk in a landfill is air space. The amount of space is directly related to the capacity and usable life of the landfill. If you can increase the air space, then you can extend the usable life of the landfill. To do this, trash is compacted into areas, called cells, that contain only one day’s amount of trash. Trash within cells are compressed by using heavy equipment (tractors, bulldozers, rollers and graders) that go over the mound of trash several times). Once the cell is made, it is covered with six inches of soil and compacted further. Cells are arranged in rows and layers of adjoining cells (lifts). In addition to compressing the trash into cells, space is conserved by excluding bulky materials, such as carpets, mattresses, foam and yard waste, from the landfill. Storm Water Drainage It is important to keep the landfill as dry as possible to reduce the amount of leachate. This can be done in two ways: • Exclude liquids from the solid waste. Solid waste must be tested for liquids before entering the landfill. This is done by passing samples of the waste through standard paint filters. If no liquid comes through the sample after 10 minutes, then the trash is accepted into the landfill. • Keep rainwater out of the landfill. To exclude rainwater, the landfill has a storm drainage system. Plastic drainage pipes and storm liners collect water from areas of the landfill and channel it to drainage ditches surrounding the landfill’s base. The ditches are either concrete or gravel-lined and carry water to collection ponds to the side of the landfill. In the collection ponds, suspended soil particles are allowed to settle, and the water is tested for leachate chemicals. Once settling has occurred and the water has passed tests, it is then pumped or allowed to flow off-site. 5 Leachate Collection System No system to exclude water from the landfill is perfect and water does get into the landfill. The water percolates through the cells and soil in the landfill much as water percolates through ground coffee in a drip coffee maker. As the water percolates through the trash, it picks up contaminants (organic and inorganic chemicals, metals, biological waste products of decomposition) just as water picks up coffee in the coffee maker. This water with the dissolved contaminants is called leachate and is typically acidic. To collect leachate, perforated pipes run throughout the landfill. These pipes then drain into a leachate pipe, which carries leachate to a collection pond. Leachate can be pumped to the collection pond or flow to it by gravity. The leachate in the pond is tested for acceptable levels of various chemicals (biological and chemical oxygen demands, organic chemicals, pH, calcium, magnesium, iron, sulfate and chloride) and allowed to settle. After testing, the leachate must be treated like any other sewage/ wastewater; the treatment may occur on-site or off-site.
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